1. Field of the Invention
The present invention relates to a voltage controlled oscillator, and more specifically to a voltage controlled oscillator composed of complementary MOS transistors.
2. Description of Related Art
Voltage controlled oscillators (called "VCO" hereinafter) have been formed of complementary MOS transistors (called "CMOS" transistors) or bipolar transistors. In general, the VCO circuits for high frequency of 5 to 10 MHz have been formed of bipolar transistors. Recenty, VCO circuits have been developed which are formed of CMOS transistors oscillating at a high frequency.
However, the VCO circuits formed of CMOS transistors have been disadvantageous in that a center frequency of a high frequency oscillation varies widely, and in that a jitter easily occurs due to digital noises superimposed on a supply voltage.
Due to the above mentioned circumstances, conventional VCO circuits generating a high frequency oscillation have been composed of bipolar transistors, and therefore, it has been considered impossible to assemble a VCO circuit within an integrated circuit.